On Wed, 2011-03-02 at 12:28 -0600, Pat Hayes wrote:
> On Mar 2, 2011, at 11:30 AM, Nathan wrote:
>
> > Jonathan Rees wrote:
[ . . . ]
> >> On Wed, Mar 2, 2011 at 5:49 AM, Nathan <nathan@webr3.org> wrote:
> >>> Jonathan Rees wrote:
> >>> now this is interesting, and I'm unsure exactly how to say it, but if we
> >>> work from HTTP Resource upwards to URI, such that we consider an HTTP
> >>> Resource as being a distinct object for which all URIs used to refer to it
> >>> are bound to that HTTP Resource (the URIs are a property of the HTTP
> >>> Resource), then we come to the wrong conclusions, and things break.
> >> No. Only TimBL's requirement that these be distinct breaks. (Maybe
> >> that's what you mean by "things" but you need to be more specific.)
> >
> > and RDF's requirement, in fact URIs is it not, that two different
> URIs refer to two different things unless explicitly stated that they
> refer to the same thing?
>
> No. RDF (and RDFS, OWL etc.) make no assumptions about unique naming.
> Any two different URIs might or might not refer to the same thing.
I hope this doesn't cause confusion, because the bottom line
semantically is what Pat and Jonathan said. But . . .
In practice almost everyone makes some degree of unique naming
assumption at one point or another. After all, when you merge two
graphs containing bnodes, and you try to collapse some of those bnodes,
but you *don't* try to collapse other URIs, then you're effectively
making a kind of unique name assumption on the other URIs. Or when you
mint your own URIs that you use within a graph, but you then merge in
some other RDF data from some other source -- say DBpedia -- and you try
to collapse some of the DBpedia URIs into your own URIs, but you do
*not* bother to try to collapse your own URIs into other of your own
URIs, then you are again making a kind of unique name assumption on your
own URIs: you knew that they represented distinct entities when you
minted them, so you didn't bother trying to collapse them.
Another way to put it is to say that in practice, applications
internally make the unique name assumption unless they have evidence (or
are told) that they can merge nodes.
Anyway, if this comment causes confusion, just ignore it. The semantics
are what Pat and Jonathan said.
--
David Booth, Ph.D.
http://dbooth.org/
Opinions expressed herein are those of the author and do not necessarily
reflect those of his employer.